High-current and high voltage MOSFETs with integrated diodes made from SiC, GaN, and other materials are useful in power electronic circuits, such as power factor correction (PFC) devices, DC-DC converters, DC-AC inverters, overcurrent and overvoltage protection circuits, and motor drives.
In many prior art SiC and GaN MOSFETs used in power electronic circuits, for example, the built-in body diode is used to carry the third quadrant/freewheeling current. However, this practice suffers from three major limitations. The body diode has a high knee voltage before the onset of conduction, leading to high conduction losses. The body diode also has a significant amount of stored charge which increases with temperature, removal of which leads to turn-on losses in adjacent devices. Finally, if the body diode is allowed to conduct, the recombination that occurs in electron-hole plasma in the device may result in progressive device degradation by causing an expansion of basal plane defects in the crystal in the case of SiC. This degradation manifests as an increase in leakage current and on-state voltage drop, causing the devices to dissipate more in losses as they age, and can eventually lead to catastrophic destruction.
Another prior art approach is to connect a separate SiC junction barrier Schottky (JBS) diode in parallel with the MOSFET to carry the third quadrant current. Yet another technique is to integrate a JBS diode within the MOSFET chip monolithically, so that, at least at typical operating currents, the forward voltage drop is less than the PN junction turn-on voltage, no bipolar injection occurs, so there is no stored charge loss, and no basal plane degradation. However, integrating a JBS diode limits the knee voltage based on the Schottky diode barrier height.